Distinct dual antiviral mechanism that enhances hepatitis B virus mutagenesis and reduces viral DNA synthesis

Lethal Mutagenesis of RNA Viruses and Approved Drugs with Antiviral Mutagenic Activity

In RNA viruses, a small increase in their mutation rates can be sufficient to exceed their threshold of viability. Lethal mutagenesis is a therapeutic strategy based on the use of mutagens, driving viral populations to extinction. Extinction catastrophe can be experimentally induced by promutagenic nucleosides in cell culture models. The loss of HIV infectivity has been observed after passage in 5-hydroxydeoxycytidine or 5,6-dihydro-5-aza-2'-deoxycytidine while producing a two-fold increase in the viral mutation frequency. Among approved nucleoside analogs, experiments with polioviruses and other RNA viruses suggested that ribavirin can be mutagenic, although its mechanism of action is not clear. Favipiravir and molnupiravir exert an antiviral effect through lethal mutagenesis. Both drugs are broad-spectrum antiviral agents active against RNA viruses. Favipiravir incorporates into viral RNA, affecting the G→A and C→U transition rates. Molnupiravir (a prodrug of β-d-N4-hydroxycytidine) has been recently approved for the treatment of SARS-CoV-2 infection. Its triphosphate derivative can be incorporated into viral RNA and extended by the coronavirus RNA polymerase. Incorrect base pairing and inefficient extension by the polymerase promote mutagenesis by increasing the G→A and C→U transition frequencies. Despite having remarkable antiviral action and resilience to drug resistance, carcinogenic risks and genotoxicity are important concerns limiting their extended use in antiviral therapy.

Detection of Oncometabolite Nicotine Imine in the Nail of Oral Cancer Patients; Predicted as an Inhibitor of DNMT1

Background:

Nicotine-metabolized product nicotine imine is suggested to play a role in metabolic changes in oral cancer. There is a significant gap in the detection of oncometabolite nicotine imine in biological fluids and nails of oral cancer patients. Oncometabolites are designated as metabolites those are usually elevated in cancer cells over normal cells. Interestingly, a direct or indirect link is missing that establishes a role of nicotine imine in pro-cancer cellular events including global DNA hypomethylation, a potential metabolic-epigenetic axis in oral cancer.

Methods:

A novel vertical tube gel electrophoresis (VTGE) system assisted purification and liquid chromatography-high resolution mass spectrometry (LC-HRMS) based identification of nicotine imine in the nails of oral cancer patients. Further, nicotine imine was evaluated for its molecular interactions with various methyltransferases including DNA methyltransferase 1 (DNMT1) by molecular docking and molecular dynamics (MD) simulations.

Results:

Data suggested the presence of nicotine imine in the nails of oral cancer patients. Molecular docking and MD simulations revealed a specific binding affinity by nicotine imine with DNMT1. Binding by nicotine imine is within the CXCC regulatory domain of DNMT1 including key residues as ARG690, PRO574, VAL658, PRO692 and ALA695. Similar binding residues are displayed by DNMT1 inhibitor 5'-Aza-2'-deoxycytidine.

Conclusion :

Nicotine imine is suggested as a predictive biomarker for oral cancer patients in nails and this finding is a first report. Molecular docking and dynamics simulation propose the role of nicotine imine as an inhibitor of DNMT1. This work supports the involvement of synergistic pro-tumor metabolic-epigenomic axis by nicotine imine that may contribute towards potential mutagenesis of normal squamous epithelium.